Thermal switch



Nov. 21, 1933- c.. W. APPELBERG THERMAL SWITCH Filed July 1G, 1931 Fly/2 Patented Nov. 21, 1933 UNITED STATES THERMAL SWITCH Carl Wilhelm Appelberg, Stockholm, Sweden, assignor to Aktiebolaget Birka Regulator, Stockholm, Sweden, a company of Sweden Application July 16, 1931, Serial No. 551,266, and in Sweden September 16, 1930 4 Claims through the deformation of a bimetallic, usually rod-shaped body. In practice, it is difficult, however, to obtain in such thermal switches a breaking speed which is sufciently high to render possible the use of thermal switches for safe control also of comparatively very large amounts of' energy. On the other hand it has been shown by practical tests that itis possible to obtain an unexpectedly rapid breaking and closing in thermal switches enclosed in. sealed receptacles by adapting the switch contact to be actuated by length variations in one or more wire-shaped or rod-shaped bodies provided with heating windings disposed in good heat transmitting con- '25 nection with the same and together with the thermal switch contact enclosed in the evacuated or gas i'llled receptacle. It has been found to be particularly advantageous to make the heat sensitive member or members in the form of thin 0 wires surrounded with heating windings, the Wires being held under tension by means of spring power and exerting a pull at a part of the contact arrangement which pull is more or less yielding when the wire is heated. The invention will be more closely described with reference to the accompanying drawing showing an embodiment of the invention. On the drawing Figure 1 represents an axial section of the thermal switch and Figure 2 a front view oi' the same.

The thermal switch is in its entirety enclosed in a hermetically sealed glass receptacle or the like 1 and is mounted on a frame 2 of insulating material, for instance steatite, which frame by 5 meanso! projecting supporting lugs, flanges or the like is rigidly held in position in the receptacle. The contact proper consists of two contact pins 3, 4 turned against each other, of which the former is secured to the free end of the longer lever arm of an angular lever 5 pivoted near the on'e end of the frame. The said longer arm of this angular lever extends substantially parallelly with the frame and is adapted to move in a longitudinal slit 6 in the frame. The contact pins 3, 4 project from opposite sides into a through- (Cl. 20G-122) going aperture 'l in the irame. The contact pin 4 is carried by a spring 8 which is secured to the frame near its upper end. The two contacts are connected to anouter circuit by means of lead out wires 9 'fused into the wallof the receptacle.

In the lever 5 and near its pivot is tapped a pin l0 on which is rotatably mounted across piece 11. Between the ends of the cross piece 1l and two pins l2 inserted in the opposite end or the frame two thin metal wires 13 are secured which are kept under tension under the inuence of a spring 17 acting on the angular lever 5. Thus the two wires 13 exert together al pull at the shorter lever arm of the angular lever 5 and tend to force the pin 3 against the pin 4. The shorter arm is formed by the pin 10 and is substantially perpendicular to the frame. Each metal wire 13 is surrounded by a .une glass tube 14 on which is wound a heating winding 15. The two heating 1 windings are mutually connected in series and are connected to an outer heating circuit by means oi fused-in terminals 16.

As long as the heat sensitive members, i. e. the thin wires 13, vmaintain normal temperature the contact pin 3 is held in contact with the counter Contact 4 by the tension ci" the wires, the counter contact 4 being then pressed backwards. Upon heating of the wires 13 through electric current in the heating winding the angular lever 5 is K turned back by means vof the spring 17 in accord- 35 ance with the expansion of the wires, the counter contact 4 initially following until a stop 18 dis- Aposed on the same abuts against the frame.

Upon continued heating the contact pin 3 moves back alone and Va rapid current interruption is obtained at this moment. p

By making the heat sensitive member or members in the form of thin wires the mass to be heated by the heating winding is reduced to a minimum, whereby the time required for heating as well as for cooling may be considerably reduced.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, since obvious modiiications Y will occur tothlose skilled in this art. c

I I claim:

1. A reversible thermal switch enclosed in a sealed receptacle and comprising an electrically isolated heat sensitive wire stretched under tenm5 sion, a. main current path, a contact controlling said main. current path, a lever carrying said contact and operable by the tension of said wire,

a heating current path independent of said main current path, a heating winding included in said no heating current path and in thermal communication with said heat sensitive Wire, but electrically separated therefrom.

2. A reversible thermal switch enclosed in a sealed receptacle and comprising a glass tube, an electrically isolated heat sensitive wire stretched under tension in said glass tube, a main current path, a contact controlling said main current path, a lever carrying said contact and operable by the tension of said Wire, a heating current path independent of said mainV current path, a heating Winding included in said heating current path and. disposed on the outside of said glass tube.

3. A reversible thermal switch enclosed in a sealed receptacle and comprising a number of electrically isolated Wires, a main current path, a contact controlling said main current path, a lever carrying said contact and operable by the tension of said wires, a heating current path independent of said main current path, a number of heating windings included in said heating current path and each in thermal communication with one of said heat sensitive wires, but electrically separated therefrom.

4. A reversible thermal switch enclosed in a sealed receptacle and comprising a number of glass tubes, a corresponding number of electrically isolated heat sensitive Wires each stretched under tension in one of said tubes, a main current path, a contact controlling said main current path, a lever carrying said contact and operable by the tension of said wires, a heating current path independent of said main current path, a number of heating windings included in said heating current path and each disposed on the outside of one of said glass tubes.

CARL WILHELM APPELBERG. 

